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the_climber
Jan 25, 2010, 8:51 PM
Post #26 of 39
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scm007 wrote: Does the strength of a bight of rope/sling/webbing/whatever vary with pull direction?
Direction of pull is irrelevant. A "bight" will simply straighten out, with no preference to direction of pull.
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jt512
Jan 25, 2010, 9:11 PM
Post #27 of 39
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scm007 wrote: So............ still haven't gotten a response.
I haven't seen a thread with so much potential since this one.
Jay
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gmggg
Jan 25, 2010, 10:05 PM
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johnwesely wrote: bigjonnyc wrote: johnwesely wrote: shimanilami wrote: johnwesely wrote: kachoong wrote: Storjon wrote: No, if all forces are in the same direction the sling is accelerating and if this acceleration is big enough air friction could possibly melt the sling and thus reduce itīs strength. A sling is either pulled or compressed. Compression loading a sling shouldnīt be a problem in a climbing situation. Regarding pulling, how many ways can you pull a sling? Think about this and the answer is obvious.. Really? Air friction? It is the new micro fracture! Dudes. Meteors burn up all the time when they re-enter the atmosphere. If you were on the space shuttle and dropped a sling, it would probably almost certainly burn up before it reached the ground. And even if it didn't, would you still trust your life to it? Case closed. I will keep that in mind when commercial space flight becomes available, and I become a millionaire. Even then I'm pretty sure they wouldn't have windows for passengers to casually open and toss slings out of on commercial space flights. Well, never mind then.
Don't despair! You can still flush one down the toilet and it might get jettisoned into the mesosphere if you're lucky.
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Adk
Jan 25, 2010, 10:17 PM
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jt512 wrote: I haven't seen a thread with so much potential since this one. Jay
Wow. What a thread! How do I measure a rope......
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rgold
Jan 26, 2010, 6:45 AM
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scm007 wrote: Say I have a 50 foot sling, and I only need a 10 foot sling. Can I just grab a 10 foot bight of rope, figure 8 it, and use it like I would a regular 10 foot sewn runner? The direction of the forces on the knot are pretty funky...
Your first question was incomprehensible, which is why you didn't get answers. This one is a bit clearer.
I don't think you have to worry about knots breaking if you are top-roping. As for a figure-eight capsizing, it will never capsize enough to work its way off a forty foot tail.
There is another problem though, and that is the knots you mentioned have a high probability of "welding" under top-rope loads, making them extremely hard to untie.
Here is what I think is a Better Way: Don't tie your long sling in one big loop. Instead, tie a small backed-up figure-eight loop on one end of your sling and leave it there permanently. When you set up a toprope, tie another small backed-up figure-eight loop wherever you need it, possibly quite far from the other end, so that clipping the two loops together (double or triple biners with gates reversed) produces the correct length sling. (Depending on the size of the anchor and the distance to the edge, you might want to wrap the sling one or more times around the anchor rather than leave a very long tail.)
The advantages are that you get exactly the length you want, the knots are loaded in the optimum direction, and each knot receives approximately half the load, making the non-permanent knot more likely to untie easily.
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knudenoggin
Jan 26, 2010, 7:03 AM
Post #31 of 39
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scm007 wrote: Cool thanks for the reply, in practice what I have is ~60 foot section of 1 inch webbing that I use for top-roping when I need to sling a tree that is a ways away from the lip. However it sure would be nice if I had a way to use this section to do whatever lip extension work I needed to for a TR. I was faced with having a 2 bolt anchor and had a lip about 10 feet down. Simply pulling the strands down and tying a figure 8 or overhand would leave me with 30 feet too much slack, so I ask what is a better system? I'm not really understanding #2 and #1 isn't practical. What I was thinking of doing was just essentially building two 10 foot slings out of this 60 footer by just grabbing any two random 10 feet sections on here and tying a figure 8 on a bight, creating 10 foot loops. But I have never loaded a figure 8 like that so I wasn't sure. My gut says that this is safe for TR'ing but I've never seen anybody do it like that. ...
There are many ways to effect the particular structure (2 independent
runners, effectively) you describe, but your solution to the particular
problem you face seems an awkward way to meet that circumstance.
Why not just tie your powerpoint as a bowline on the bight and
tie off the ends to the bolts (or clip a bight to one, tie off other)?!
And the slack hangs at the tied-off bolt. Adjusting a 2-legged eye knot
will be simpler than what you're asking about.
(As for forming those independent runners, you can tie them with any
of: butterfly, sheet bend, reversed sheet bend, Frost knot, sheepshank
(topologically), and a sort of SmitHunter's bend. E.g., with the Butterfly,
that knot's "eye" ("loop") would be the slack, ultimately.)
dugl33 wrote: Edit to add, one more time: EDK style loading on figure eights, whether tied in rope or webbing, has been shown to fail at low levels of loading. Figure eights loaded this way roll indefinitely. I think knot nerds call it "capsizing". ...
It's actually a subset of capsizing, flyping, to be precise.
But I'm unaware of any evidence of this behavior in webbing?!
Looking at the knot in tape, the different geometry and the typical
low stretch suggest that it will be stable until breaking -- which, IIRC
one fellow's testing of it (posted to RC.com), is somewhere well south
of the Water knot's strength.
The "rolling (flyping) indefinitely" is also a bit of a question: the testing
that has been conducted has been with institutional slow-pull devices
which give a constant rate of pull, with a load drop-off on the flype
and then resumed tension; in practice, the force of a fall would take a
cut in making the initial flype (if ...), and subsequent loading would be
diminished -- same mass, less momentum!? OTOH, there is some bit
of "shock loading", though w/dynamic rope, not much. I don't think that
there has been testing with a falling mass. (Yes, there was one tragedy
-- using very stiff rope.)
*kN*
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dugl33
Jan 26, 2010, 4:27 PM
Post #32 of 39
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scm007 -- I think we've all managed to overcomplicate your question. So, after a good nights sleep, this is what I've come up with:
I propose you end up with this --
Overview
it's simple... it's solid ... the loops are redundant ... its equalizing
The procedure is as follows:
1.) Grab both tails of your 50' feet of webbing, and work back to the center, making the webbing neat and flat as you go. This is the upper left point of the "V". (Edit: You could premark this point with a little rub-a-dub ink or tape to save time)
2.) Using your arms, measure for length (for most people this is 5'-6' per stroke). Tie a simple overhand knot here. This is the upper right point of the "V".
3.) Grab this overhand knot, and your original left side loop end, and work back to the center. Tie two overhand knots, each about 6 inches from the center point.
Now you basically have an equallete. No fuss, no muss.
The detail at the master point...lockers might be better.
The detail at the upper right of the "V"
I believe any wierdness loading the knot at the "crotch" is of little consequence in this application.
 Cheers
Edit to add: alternate detail for the upper right side of the "V". No "crotch" loading. I think I like this a little better.
Alternate upper right
(This post was edited by dugl33 on Jan 26, 2010, 6:28 PM)
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desertwanderer81
Jan 26, 2010, 5:32 PM
Post #33 of 39
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This thread makes me happy.
All is right in the world.
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dugl33
Jan 26, 2010, 6:07 PM
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As a follow up, perhaps adatesman or someone else in The Lab could perform the following tests (or provide the appropriate link, if previously tested)
Using 1" tubular webbing
1.) overhand knot, "crotch" loaded
2.) overhand knot "EDK" loaded
3.) figure eight, "crotch" loaded
4.) figure eight, "EDK" loaded
simple water knot for control group.
Same tests in dyneema or other materials = bonus round.
(I did find the previous webbing knot testing thread, but to my knowledge these particular tests were not conducted.)
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scm007
Jan 26, 2010, 6:31 PM
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That looks pretty cool dugl33, thanks a ton for your replies. I would be very interested to see the results of these tests as well.
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j_ung
Jan 26, 2010, 11:27 PM
Post #36 of 39
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shimanilami wrote: johnwesely wrote: kachoong wrote: Storjon wrote: No, if all forces are in the same direction the sling is accelerating and if this acceleration is big enough air friction could possibly melt the sling and thus reduce itīs strength. A sling is either pulled or compressed. Compression loading a sling shouldnīt be a problem in a climbing situation. Regarding pulling, how many ways can you pull a sling? Think about this and the answer is obvious.. Really? Air friction? It is the new micro fracture! Dudes. Meteors burn up all the time when they re-enter the atmosphere. If you were on the space shuttle and dropped a sling, it would probably almost certainly burn up before it reached the ground. And even if it didn't, would you still trust your life to it? Case closed.
Coincidentally, this is also the reason why dogs will never be allowed on the space shuttle.
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j_ung
Jan 26, 2010, 11:30 PM
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Their heads would burn off during re-entry.
<rimshot>
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dugl33
Jan 27, 2010, 2:23 AM
Post #38 of 39
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j_ung wrote: shimanilami wrote: johnwesely wrote: kachoong wrote: Storjon wrote: No, if all forces are in the same direction the sling is accelerating and if this acceleration is big enough air friction could possibly melt the sling and thus reduce itīs strength. A sling is either pulled or compressed. Compression loading a sling shouldnīt be a problem in a climbing situation. Regarding pulling, how many ways can you pull a sling? Think about this and the answer is obvious.. Really? Air friction? It is the new micro fracture! Dudes. Meteors burn up all the time when they re-enter the atmosphere. If you were on the space shuttle and dropped a sling, it would probably almost certainly burn up before it reached the ground. And even if it didn't, would you still trust your life to it? Case closed. Coincidentally, this is also the reason why dogs will never be allowed on the space shuttle.
The ratio of mass to surface area for a meteor is typically quite high, whereas this ratio for a sling is much lower. It will take a good deal more atmospheric friction over a greater period of time for a meteor to adjust to terminal velocity as it barrels toward earth. Additionally, it may adjust to a particular orientation of least resistance, concentrating friction on the leading side. Some, however, do indeed arrive intact as can be seen by various earth craters.
Slings on the other hand, may potentially survive due to the lower mass to surface area ratio and a tendency to fall in a chaotic fashion, with the end result being a lack of concentrated atmospheric friction on any one point, perhaps with the exception of the bar-tacks. Much less force (opposite and equal atmospheric friction) will be required to decelerate the sling, characteristic time to achieve Tvelocity will be less and terminal velocity / impact velocity will be modest.
Now, if you chuck it out of the shuttle with a biner attached, or perhaps your dog, all bets are off.
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kachoong
Jan 27, 2010, 1:41 PM
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j_ung wrote: Their heads would burn off during re-entry. <rimshot>
I believe, Jay, that it would instead be the leash that burns up on re-entry and we don't want shuttle dogs to get away and roam space now, do we?
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